My second wife and I were in our late 20's, married for 2 years. She had a younger sister who was 13 at the time. Just started growing tits and developing an hour glass figure. She always wore tight clothing and all was there to see.
Wife and I always liked dirty talk when we had sex. I was always telling her I wanted to fuck her sister and it really turned her on.
There was a time her sister came to spend the week-end with us. We had only 1 bedroom suite which we slept in. There was a couch in the living room but it was very uncomfortable. When it was bed time it was decided the wife and her sister would sleep in the bed and I would sleep on a pallet next to the bed. The only problem with that is that we had hard wood floors which were very cold. Some time thru the night I woke the wife and told her I was getting in the bed. She said OK get between us. That was good for me as I could get close to her sister. I was wearing jockey shorts and nothing else. When I got in bed her sister turned on her side and move her butt back against me.
We were closer than we had ever been before. I laid my hand on her thigh and rubbed just a little. I wanted to fuck this beautiful girl but knew I couldn't because she was only 13 at the time. I turned to my side and rubbed my hard cock against her ass. Wife took notice and reached over me and started jacking me off with the head if my dick rubbing her sisters ass. Wife raised sisters night gown and my cock was right at the entrance to her pussy. The only thing between my cock and her cunt was her panties.
Wife kept jacking me and when I climaxed I shot cum into the crotch of her sisters panties between her legs. That made wife so horny she made me take her to the living room and fuck her. That night was really hot.